What's a container? Containers let you store and access collections of values of the same type, yes arrays let you do the same thing but the SDL containers offer more flexibility and power than an array.
The algorithms - defined in the STL work with its containers. The algorithms are common functions that programmers find themselves repeatedly applying to groups of values. they include algorithms for Sorting, Searching, copying, merging, inserting and removing container elements. The cool thing is that the same algorithm can work its magic on many different container types.
Iterators - Iterators are objects that identify elements in containers and can be manipulated to move among elements. they're great for iterating through containers in addition, Iterators and required by the STL algorithms.